I know there is some adult anime that can't be steam here, but I found some new anime that airing right now and they aren't here. I kind of understood how anime that already have been streamed here then after awhile some old anime kept and others dropped. How does crunchyroll choose which new anime to stream?

I would assume that they look at what they expect to be big, the obvious ones and try their hardest to get those. Once they have those they look at the studios who are friendly to the idea of western simulcasts and approach them to see what they're willing to offer and for what price. They look at how much they expect they'll make vs the cost then gopher it or not. This is what I would assume, obviously given you're dealing with japanese companies expect logic and rationality to fly out the window somewhere along the line

It all depends on home distributors and tv networks. If Funimation takes an anime, usually they take it exclusively for them so those shows are out of Crunchys hands. TV Tokyo owns a part of CR so they try to get as many shows that they have on here. And CR basically they try to get everything else.

I know there is some adult anime that can't be steam here, but I found some new anime that airing right now and they aren't here. I kind of understood how anime that already have been streamed here then after awhile some old anime kept and others dropped. How does crunchyroll choose which new anime to stream?

CR has stated before they don't pick and chose. The put in a offer for everything streaming for a season. There is always the possibility of the licensor for a series rejecting any bid for a simulcast out of hand. They may also only offer it in conjunction with a home video license, which puts CR out of the running.

Once past that stage, CR determines how well the series is likely to perform, and makes an offer. I'm not certain if the amount paid per stream varies much if at all, but the minimum guarantee does. The minimum guarantee means that if a series were a flop, and only a couple of hundred people on average streamed each episode, the licensor would still get $x (equivalent to a greater number of streams).

At this point the licensor could reject that amount as too low, at which point CR could either reconsider or decide the series would lose them money. They could also be outbid for the series. (Per rumor, the reason AoD had been getting series for the UK is because they are outbidding CR [and losing money in doing so]).

There is also the fact that a company like Funimation could bid the same for a series, but sweeten the deal by saying, "If streaming numbers are good enough (and possibly even commit to a target figure), we will license the series for home video", or they could just opt to add in the home video license out of the gate (at which point CR is clearly outbid).